Downhole valves are used to isolate portions of the wellbore for a variety of reasons such as for safety systems or to allow building a long bottom hole assembly in the wellbore, to name a few examples. Such valves have featured a rotating ball with a bore through it that can be aligned or misaligned with the path through the tubing string where the valve is mounted. The ball is surrounded by a sliding cage that is operated by a hydraulic control system from the surface. One such design features opposed pistons actuated by discrete control lines. This design was concerned about a pressure imbalance on an operating piston and provided a passage through the piston with two check valves 54, 76 in series to allow pressure equalization across the actuating piston with the ball in the closed position.
What can happen in this type of a ball valve that has upper and lower seats against the ball in the closed position is that pressure from downhole can rise, which leads to a pressure differential between the passage inside the ball and the downhole pressure. This pressure differential can distort the ball and make it hard or impossible for the piston actuation system to operate the ball back into the open position. One way this was solved is described in a commonly assigned application Ser. No. 12/366,752 filed on Feb. 6, 2009 and having the title Pressure Equalization Device for Downhole Tools. The solution described in this application was to use a tool that goes into the upper sleeve that hold a seat against the ball and separate the seat from the ball while providing pressure from the surface at the same time to equalize the pressure on the ball before trying to rotate it to the open position. The problem with this technique was that it required a run into the well with coiled tubing, latching and shifting the upper sleeve and associated seat enough to give access into the ball for equalizing pressure. One of the downsides of this technique was that the pressure admitted to try to equalize the pressure in the ball could be high enough to unseat the lower seat from the ball so that the higher pressure below the ball would get to above the ball. This technique also took time which cost the operator money and required specialized equipment at the well location, which could be remote or offshore and add yet additional costs to the effort to operate the ball when subjected to high differential pressures that could distort the ball enough to make it hard for the hydraulic system to rotate it.
In flapper type safety valves such as U.S. Pat. No. 5,564,502 the preferred method to get pressure equalization on a closed flapper was to simply apply tubing pressure on top of it to reduce the differential before using the control system to try to rotate the flapper. Of course, the flapper is built to rotate open with pressure applied above so that this technique did not equalize pressure around the flapper when it was closed but simply built up pressure above it when it was closed. Other equalizer valves mounted in the flapper were actuated by the hydraulic system moving down a flow tube that impacted the equalizing valve before the flapper was engaged by the flow tube as seen in U.S. Pat. Nos. 6,848,509 or 4,478,286.
The present invention manages to equalize pressure by simple application of pressure from the surface that can communicate to inside the ball in the closed position for pressure equalization. That pressure communicated through a passage in the housing that selectively communicates the zone above the closed ball to the isolated passage within the ball when the ball is in the closed position. That communication preferably occurs through a check valve assembly that preferably has a series redundant feature and screens to assure that on removal of the applied pressure that the check valve passage will reclose allowing for normal ball operation to open the ball with the hydraulically actuated operating piston or pistons. These and other features of the present invention will be more readily appreciated by those skilled in the art from a review of the specification and associated drawings while understanding that the full scope of the invention is to be found in the appended claims.